1. Field of the Invention
The present invention relates to a printing apparatus capable of printing on a plurality of types of sheets, and a control method thereof.
2. Description of the Related Art
An electrophotographic printing apparatus needs to apply heat and pressure to a sheet in order to fix, to the sheet, toner or ink transferred on it. For this purpose, the electrophotographic image forming apparatus includes a fixing unit for applying heat and pressure to a sheet and a conveyance mechanism for conveying a sheet to the fixing unit.
The amounts of heat and pressure necessary to fix toner or ink onto a sheet change depending on sheet characteristics such as the thickness and surface property of a sheet. The printing apparatus therefore requires a mechanism for changing the heating temperature of a sheet by the fixing unit, and control of the heating temperature of a sheet using a combination of fixing units. As a mechanism for performing appropriate fixing control in accordance with sheet characteristics, for example, Japanese Patent Laid-Open No. 07-072678 discloses a method of performing a printing process by setting a fixing unit to a set value at which toner or ink can be fixed to a sheet printed by a print job.
However, the conventional technique suffers the following problems. When successively printing on a plurality of sheets with different characteristics, the control of the fixing unit needs to be changed at the sheet switching timing. For example, the temperature of a fixing roller for heating a sheet needs to be changed in accordance with sheet characteristics. In this case, a standby time may be generated to change the temperature of the fixing unit, interrupting the printing process and decreasing the printing throughput.
Also, for example, when the fixing unit has the same settings for all types of sheets to be printed by a print job, an extra burden may be put on the fixing unit depending on a combination of sheet types. Further, the service life of the fixing unit may shorten. More specifically, when printing on sheets greatly different in characteristic (e.g., grammage) between former and latter pages of a print job, the same setting (e.g., the same fixing temperature) is applied to the entire job according to the conventional technique. Even when the burden on the fixing unit differs between the former and latter parts of the print job, all pages need to be printed using a setting which increases the burden. An unwanted burden is put on the fixing unit, so the service life of the fixing unit may shorten.